"It shows a lack of understanding of the rawness of the nerve endings in the countryside, given the reaction to BSE.

"You would have thought every nerve ending, every hair on the back of their necks would have risen, whatever the result.

"Instead Defra are totally silent the next day and you begin to wonder who is running the show.

"We have them presenting Lord Haskins's report on the rural economy yesterday when here was an issue which could blow the whole rural economy right apart."

A meeting of the Government's spongiform encephalopathy advisory group (Seac), which was due to discuss the results today, has had to be cancelled.

Prof Peter Smith, chairman of Seac said: "We were all completely amazed when the Government laboratory said it could not find any trace of ovine material. It is a fairly disastrous error. It is an amazing result that no one expected."

The study, which cost £217,000, was commissioned by the now defunct Ministry of Agriculture in 1997.

A soup of homogenised brain, supposedly gathered from 2,867 sheep showing symptoms of scrapie, an illness very similar to BSE, was sent to Edinburgh.

The institute said it had expressed concern that the samples might have been contaminated with bovine material when they were gathered for a different purpose in the early 1990s.

He explained that the institute could not test DNA, which would have shown whether the brains belonged to sheep or cows.

Both the institute and Defra have launched independent studies into how the mistake occurred. These are likely to look at a possibility of a labelling error in the freezers where the samples were kept.

The one positive aspect of the affair is that the national flock is safe for the foreseeable future.

John Thorley, the chief executive of the National Sheep Association, said: "I am delighted that this is the outcome. There is no evidence that there is one shred of BSE in sheep."